Why won't my Blackberry open LO .doc?

I’ve seen this question asked before, but can’t see that it’s been satisfactorily answered…

I’m currently using LO 4.0.4.2, saving as .doc or .dotx to edit with Documents to Go on my Blackberry. This has worked without issue in the past (3.4 and lower), now it tells me “This file cannot be opened because it is not a valid MS Word 97-2008 file.” I spend a fair amount of time waiting in school parking lots for my daughter, and really need to be able to edit from my phone. Any help would be greatly appreciated!

Thanks’
-mike